GCN Circular 38776
Subject
GRB 250101A: GMG spectroscopic redshift at z ~ 2.481
Date
2025-01-02T10:05:57Z (7 days ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
email
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, S.-S. Li, H. Lin and J.-M. Bai (YNAO, CAS) report:
We observed the optical counterpart of GRB 250101A (Page et al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin and Spiridonova, GCN 38762; Odeh and Guessoum, GCN 38763; Hu et al., GCN 38764; Moskvitin et al., GCN 38765; D’Avino and Izzo, GCN 38768; Escudero-Coca et al., GCN 38769; Leonini et al., GCN 38771). The observation was conducted using the GMG-2.4m telescope with Grism #14, which provides a wavelength coverage of 3600–7460 AA. A single 1800s spectrum was obtained, with exposure beginning at 14:24:54.5 UT on 2025-01-01, about 1.03 hours after the Swift trigger.
The Ly-alpha absorption feature at ~ 4250 AA is evident. Despite the low signal-to-noise ratio of the spectrum, we identified multiple metal absorption lines: Si II at 1303 AA, C II at 1335 AA, Si IV at 1394 AA, Si IV at 1403 AA, C IV at 1549 AA, Al II at 1671 AA, Al III at 1855 AA, and Al III at 1863 AA. These metal absorption features consistently indicate a redshift of z ~ 2.481, which is consistent with the Xinglong-2.16m result (Zhu et al., GCN 38759).
We acknowledge the staff at the Lijiang Observatory for conducting the observation.